This invention relates to an intercommunication apparatus and, in particular, to an intercommunication apparatus for carrying out communication between a LAN (Local Area Network) emulation (hereinafter called LANE) terminal and an IP (Internet Protocol) over ATM (Asynchronous Transfer Mode) (hereinafter called IPOA) terminal.
In LANE, provision is made of a mechanism for converting a destination MAC (Media Access Control) address of a particular MAC frame into an appropriate ATM address (resolving the MAC address to obtain the ATM address). MAC frame transfer on a conventional Ethernet is emulated on an ATM network.
On the other hand, in IPOA, provision is made of a mechanism for converting a destination IP address of a packet in a particular network layer into an appropriate ATM address (resolving the IP address to obtain the ATM address) and the packet in the network layer is directly transferred on the ATM network.
As described above, the LANE and the IPOA are different in object and approach of address resolution from each other. Therefore, a LANE terminal and an IPOA terminal can not simultaneously coexist in a same subnetwork.
Therefore, in a particular subnetwork, it is impossible, for example, to operate an ordinary terminal in the LANE while a particular service (for example, a video-on-demand service) is operated by the IPOA terminal.
It is an object of this invention to provide an intercommunication apparatus which allows a LANE terminal and an IOPA terminal to simultaneously coexist in a same subnetwork.
In order to achieve the above-mentioned object, there is provided an intercommunication apparatus for carrying out communication between one and another of LAN (Local Area Network) emulation terminals and IP (Internet Protocol) over ATM (Asynchronous Transfer Mode) terminals, the apparatus comprising:
an IPOA (IP over ATM) server which stores information related to the IP over ATM terminals;
an encapsulating portion for encapsulating input data;
a frame converting portion for carrying out, by the use of the information stored in the IPOA server, interconversion between MAC (Media Access Control) frame encapsulation data and LLC/SNAP (Logical Link Control/SubNetwork Attachment Point) encapsulation data prepared by the encapsulating portion; and
a bridge portion for exchanging data between the LAN emulation terminals and the frame converting portion.
The frame converting portion comprises:
a MAC frame input/output portion for input and output of data to and from the bridge portion;
an address table connected to the IPOA server and holding information including an IP address, a MAC address, and an ATM address as entries;
an ARP (Address Resolution Protocol) processing portion connected to the address table for preparing and resolving an ARP request; and
a frame processing portion responsive to an IP packet supplied thereto for searching the MAC address in the address table to acquire the ATM address.
There is also provided a communication method for carrying out communication between one and another of the LAN emulation terminals by the use of the above-mentioned intercommunication apparatus, the method comprising:
a step of transmitting the ARP request designating the IP address of a reception terminal of the LAN emulation terminals from a transmission terminal of the LAN emulation terminals to other LAN emulation terminals by a LANE (LAN emulation) protocol;
a step of preparing, in the reception terminal, an ARP reply including the MAC address of the reception terminal, and transmitting the ARP reply to the transmission terminal by communication using the LANE protocol; and
a step of preparing, in the transmission terminal, a MAC frame containing the IP packet to be transmitted to the reception terminal by the use of the MAC address contained in the ARP reply transmitted from the reception terminal, and transmitting to the reception terminal the MAC frame thus prepared.
There is also provided a communication method for carrying out communication between one and another of the IP over ATM terminals by the use of the above-mentioned intercommunication apparatus, the method comprising:
a step of transmitting from a transmission terminal of the IP over ATM terminals through the encapsulating portion to the IPOA server an address resolution request for converting the IP address of a reception terminal of the IP over ATM terminals into the ATM address;
a step of encapsulating and transmitting, in response to the address resolution request transmitted from the transmission terminal, an address resolution reply containing the ATM address of the reception terminal from the IPOA server through the encapsulating portion to the transmission terminal; and
a step of transmitting the IP packet to the reception terminal by the use of the ATM address of the reception terminal contained in the address resolution reply.
There is furthermore provided a communication method for carrying out communication from a transmission terminal being one of the LAN emulation terminals to a reception terminal being one of the IP over ATM terminals by the use of the above-mentioned intercommunication apparatus, the method comprising:
a step of registering, in said IPOA server, IP address and ATM address information of said reception terminal;
a step of transferring to said address table the IP address and the ATM address information of said reception terminal registered in said IPOA server;
a step of extracting, in said address table, the MAC address of said reception terminal from an ESI (End System Identifier) field of the ATM address of said reception terminal and storing the information of the IP address, the MAC address, and the ATM address of said reception terminal;
a step of transmitting, from said transmission terminal through said bridge portion and said MAC frame input/output portion to said ARP processing portion in accordance with a LANE (LAN emulation) protocol, the ARP request designating the IP address of said reception terminal;
a step of resolving, in said ARP processing portion, said ARP request, detecting the MAC address of said reception terminal from said address table by the use of the IP address of said reception terminal as a target IP address in the ARP request, preparing the ARP reply containing the MAC address, and transmitting it to said transmission terminal through said MAC frame input/output portion and said bridge portion;
a step of preparing, in said transmission terminal, the MAC frame containing the IP packet to be transmitted to said reception terminal in response to the ARP reply, and transmitting it to said frame processing portion through said bridge portion and said frame input/output portion;
a step of detecting, in said frame processing portion, the ATM address of said reception terminal from said address table with reference to the MAC address contained in the MAC frame, and transmitting the ATM address and the IP packet to said encapsulating portion; and
a step of encapsulating, in said encapsulating portion, the IP packet and transmitting it to said reception terminal.
There is also provided a communication method for carrying out communication from one of the IP over ATM terminals to one of the LAN emulation terminals by the use of the above-mentioned intercommunication apparatus, the method comprising:
a step of transmitting, to the IPOA server through the encapsulating portion from a transmission terminal which is the one of the IP over ATM terminals, an address resolution request for converting, into the ATM address, the IP address of the reception terminal which is the one of the LAN emulation terminals;
a step of encapsulating and transmitting, in response to the address resolution request transmitted from the transmission terminal, an address resolution reply containing an ATM address assigned to the encapsulating portion from the IPOA server through the encapsulating portion to the transmission terminal;
a step of encapsulating, in the transmission terminal, the IP packet desired to be transmitted and transmitting it to the encapsulating portion;
a step of extracting, in the encapsulating portion, the IP packet from reception data and transferring it to the frame processing portion;
a step of transmitting from the frame processing portion to the ARP processing portion the IP address of the reception terminal in order to ask the MAC address of the reception terminal;
a step of preparing, in the ARP processing portion, the ARP request containing the IP address of the reception terminal unless relevant information is held therein, and transmitting the ARP request through the MAC frame input/output portion and the bridge portion to the reception terminal with a destination MAC address as a broadcast address;
a step of preparing, in the reception terminal, an ARP reply containing the MAC address assigned to the reception terminal in response to the ARP request, and transmitting the ARP reply through the bridge portion and the MAC frame input/output portion to the ARP processing portion in accordance with the LANE protocol;
a step of obtaining, in the ARP processing portion, the MAC address of the reception terminal from the ARP reply to transmit the MAC address of the reception terminal to the frame processing portion;
a step of transmitting, in the frame processing portion, the IP packet as communication data to the MAC frame input/output portion with the MAC address of the reception terminal as the destination MAC address; and
a step of encapsulating, in the MAC frame input/output portion, the IP packet transmitted from the frame processing portion into the MAC frame, and transmitting it to the reception terminal through the bridge portion.
In this invention having the above-mentioned structure, interconversion is carried out between the MAC frame encapsulation data and the LLC/SNAP encapsulation data by the use of the information related to the IPOA terminal and registered in the IPOA server. Therefore, the LANE terminal and the IPOA terminal are allowed to coexist in a same subnetwork.